1. Field of the Invention
The present invention relates to image forming apparatuses and control methods thereof, and particularly relates to image forming apparatuses and control methods thereof in which gradation characteristics of an image are corrected.
2. Description of the Related Art
Conventionally, image forming apparatuses that employ an electrophotographic method (particularly color copiers or laser beam printers or the like that use color toners of a plurality of colors) are provided with lookup tables (“LUTs”) for converting image signals to signal values corresponding to characteristics of its image forming engine so as to obtain desired density gradations. In the case of a color copier for example, a LUT is provided for the colors of yellow (Y), magenta (M), cyan (C), and black (K) respectively, and a desired full color image can be output by optimizing the signals of each color using the respective LUT.
Generally, the gradation characteristics of electrophotographic method image forming apparatuses change undesirably due to change over time. Accordingly, in a case where usage of the apparatus will extend over a long period for example, it is preferable that the LUTs for adjusting gradation characteristics held inside the apparatus are regenerated with a timing such as when the apparatus is started (see Japanese Patent Laid-Open No. 2000-238341 for example).
Generally, in creating LUTs for adjusting gradation characteristics in electrophotographic method image forming apparatuses, time is required for creating density measurement patches on an image carrier such as a photosensitive drum, an intermediate transfer member, or a recording paper, and for measuring these patches. Consequently, since it is necessary to generate and measure a very large number of patches to generate LUTs with high accuracy, the time taken in the process of generating LUTs increases undesirably for greater numbers of patches.
The aforementioned conventional process of regenerating LUTs is carried out, for example, after power to the image forming apparatus is turned on or after a long period of no use. For this reason, there is a problem in that image forming processes cannot be carried out during the process of regenerating LUTs, which undesirably generates so-called wait times.